Adsorption of n-Alkanes on Silicalite Crystals. A Temperature-Programmed Desorption Study

The adsorption mechanism of n-alkanes on silicalite has been studied by a modified temperature-programmed desorption (TPD) technique. These experiments are performed by thermogravimetry at constant hydrocarbon partial pressure and at slow heating rate. This work establishes the reversibility of the adsorption equilibrium, and it is demonstrated that TPD experiments occur under conditions that are very close to equilibrium. A quasi-chemical approach taking into account different adsorption sites provides a good modeling of the TPD curves. Sorption enthalpy and entropy variations of n-alkanes are obtained. The sorption data for n-butane to n-octane are in good agreement with adsorption literature data. Moreover, they provide relevant information on the adsorption mechanism and show that entropic effects are predominant.